Inferno: Oasis of Koessa is an adventure module from Paul Elkmann and Geoffrey O. Dale, the latter known to old school gamers as the author of the Inferno hex crawl for Judges Guild, which was literally set in hell as envisioned by Dante. That only had 4 circles of hell, but he included a 5th circle in one of the issues of Fight On! and then apparently finished the rest in a stand alone product.
As the name implies, Inferno: Oasis of Koessa is set in hell (the 7th Circle), basically a small oasis consisted of some sphinxes, a funerary temple, a tower (obelisk), and some small pyramids, ruled over by a mummy king. In practice, it's a collection of dungeons. The largest is a sphinx, with just over 100 keyed locations and 20 pages. The funerary temple is 14 locations and 5 pages, the tower 11 floors (one per floor) and 4 pages, the tomb is 16 locations over 6 pages, and the pyramids are about 12 locations and 5 pages each.
For the most part, all of these places are old school dungeon crawls. Very old school, they very easily could have come out of a Judges Guild product circa 1980 (as did the original Inferno). Lots of combat, lots of death traps (two or three saving throws per room seems to be about the norm), with the occasional very strange thing that makes you laugh and say "That's crazy!". My favorite example of the latter is a dwarf polymorphed into a chimp that throws bananas at the PCs, some of which explode.
